The present invention relates generally to blast furnace stoves and in particular to an improved blast furnace stove construction.
Blast furnace stoves, sometimes referred to as hot blast stoves, are employed in iron making to preheat the combustion air before entry into a blast furnace. Typically, a blast furnace stove will be a silo-shaped structure, constructed of refractory and insulating brick, and surrounded by a metal shell. Adjoining combustion and regenerative chambers are defined by a vertically extending internal dividing wall also constructed of refractory materials. The chambers communicate through a passage formed by a domed top.
The regenerative chamber, more commonly called checker chamber, includes tiers of refractory brick having aligned flow passages which extend from the top to the bottom of the chamber. The purpose of the checkerwork is to absorb and store heat from hot exhaust gases which pass through the checkerwork during a heating cycle. During this cycle, exhaust gases from an associated blast furnace are introduced and burned in the combustion chamber. The hot gases flow upwardly in the combustion chamber and then travel downwardly through the checkerwork, finally exiting at the bottom of the checker chamber. Once the checkerwork has attained a predetermined temperature, the heating cycle is terminated and the blast cycle begins.
In the blast cycle, outside air is introduced at the bottom of the checker chamber and travels upwardly through the checkerwork absorbing the stored heat. This preheated combustion air then travels down through the combustion chamber exits the stove and enters the blast furnace.
The internal operating temperature in the blast stove varies considerably and is well in excess of 2000.degree. F. in certain portions of the chamber. For this reason, the outer wall of the blast stove must be heavily insulated. The insulation requirement for the outer wall, however, varies with the vertical height. The reason for this phenomonon is due to the operating nature of the blast stove. During the heating cycle, the hot gases which travel down through the checkerwork gradually cool during their descent. Consequently, the upper portions of the checkerwork will generally reach temperatures much higher than the lower portion of the checkerwork. This vertical temperature gradient which exists in the checker chamber during normal operation necessitates added insulation in the upper regions of the blast stove.
The prior art blast stove constructions have generally chosen a rather inefficient method for providing the needed additional insulation. The peripheral wall of a typical prior art stove is of a uniform thickness throughout its height and is constructed of refractory, insulating and metallic materials. Specifically, it will include a refractory ring wall surrounded by a metal shell and further include insulation between the shell and the ring wall. Because the upper regions of the blast furnace stove will require added insulation, the refractory ring wall in this region will include both "hard brick" and "insulating brick." The lower region of the blast stove, requiring less insulation, would include only hard brick. The thickness of this hard brick wall, however, would be equivalent to the total thickness of the hard brick and insulating brick wall employed in the upper region of the blast stove where more insulation was required. Thus, the added thickness of the lower portion of the blast stove wall merely serves to support the added insulating brick used in the upper portion of the blast stove. The increased thickness of the lower portion of the blast stove wall not only added unnecessary cost to the stove but more importantly reduced the volume of the checker chamber which lowered the total thermal capacity of the chamber. The need for adequate wall thickness to provide the necessary insulation coupled with the negative effect wall thickness has on checker chamber volume resulted in compromised constructions in prior art blast stoves. It has been found desirable to increase the checker chamber volume, if possible, without increased cost. Existing blast stoves are generally designed to operate up to twenty-five years before complete rebuilding. For the most part, the external dimensions of these blast stoves cannot be enlarged because their base area is constrained by the hardware and plumbing communicating with the blast furnace and located near the bottom of the stove. It is usually impractical to increase the overall diameter of the blast stove at the base to provide additional checker chamber volume. In the past, the prior art blast stoves have been renewed without change, and no improvement in checker chamber volume was realized as a result of rebuilding. Moreover, in cases where the blast stove diameter could be enlarged (i.e., a new installation) the expensive prior art construction method was retained, that is, the ring wall of the lower portion of the blast stove included an added thickness to support the insulating brick used in the upper portion of the stove.